If extraterrestrial life is visible every night on television and in the cinema, it has never been seen in space. Not even a microbe, dead or alive, let alone a wrinkled-faced Klingon.
Despite this absence of protoplasmic presence, many researchers – sober and skeptical academics – believe that life beyond Earth is ubiquitous. According to them, the proof could be provided within a generation. These scientists back their sunny point of view with a few astronomical facts that were unknown a generation ago.
In particular, and thanks in large part to the success of NASA’s Kepler space telescope, we can now safely say that the universe is full of temperate worlds. Over the past two decades, thousands of planets have been discovered orbiting other stars. New planets appear at the rate of at least one per day.
Their abundance is more impressive than the number of planets. It seems that the majority of stars have planets, which implies the existence of a trillion of these small bodies in the Milky Way galaxy alone.
Further analysis of the Kepler data suggests that as many as one in five stars could harbor a particular type of planet, the same size as Earth and with similar average temperatures. These planets, described as “habitable”, could be enveloped in an atmosphere and abound in liquid water.
In other words, the Milky Way could host tens of billions of Earth’s cousins.
A barren universe?
It is difficult to accept that all these worlds are barren, a circumstance that would make us, and all the flora and fauna of our planet, a miracle. Miracles have little place in science.
Of course, just because there’s a lot of attractive cosmic real estate doesn’t mean finding dwellers would be easy. There are only three ways to do this, and they all depend on sophisticated and expensive experiments.
First, we could find life nearby. Real efforts are being made in this direction, particularly in the context of our reconnaissance of Mars. So far, most of the research has been indirect: we’ve deployed rovers whose job it is to locate the best places to dig into the Red Planet and possibly discover fossil or existing microbes beneath the barren surface.
It’s not about trying to find life. They are attempts to find places where life could be found. Progress is deliberate, and it’s slow.
Without a doubt, Mars remains the favorite bet of biologists. Nevertheless, some experts prefer to bet on the moons of Saturn and Jupiter. At least five of these satellites seem to harbor muddy environments, mainly liquid water, but also natural gas in the case of Titan.
Then again, the kind of life that could best thrive on these moons would be microscopic. Detecting its presence could be done in a number of ways, ranging from simple overflight missions that capture the fumes from natural geysers, to sending elaborate drilling rigs to penetrate the 15 km of ice that separates the surface from Europa. , moon of Jupiter, gigantic seas that lie below.
Unfortunately, much of this reconnaissance hardware is still on the drawing boards, not in space. Progress is slow, mainly because funding is low.
A second method to find biological evidence is to analyze the atmospheres of planets around other stars. To do this, we use a traditional technique of astronomy, spectroscopy, which would allow researchers to know the composition of an atmosphere several light years away.
If an experiment to find oxygen or methane in the air of another planet is simple to describe, it is difficult to carry out. Indeed, the planets are not very luminous, whereas the stars around which they revolve are.
Various solutions to this problem have been devised, including orbiting multiple-element telescopes and giant occulters in space. It’s rocket science, but it’s not as difficult as curing a common cold. Engineers could build this stuff in a dozen years, but only if they had the money.
The third approach to finding biology beyond Earth is to search beyond microbes for intelligent life by listening for radio signals or flashing laser lights. More antennas and better receivers could accelerate this research, but again funding is the limiting factor.
In summary, we are not certain that there is life in space, but the circumstances of the universe certainly suggest that this idea is plausible. Discovering it would be extraordinarily exciting, but since the payoff is uncertain, the investment in research has been modest.
Of course, if you don’t put your hand in your pocket, you will never win the jackpot. And it is a matter of will.
Seth Shostak, principal astronomer of the SETI Institute.